Collaborative Research: Chemical, Physical, and Radiative Properties of North Atlantic Free Tropospheric Aerosol after Long-range Transport
The radiative forcing of aerosol is not determined solely by local sources and fresh emissions, but also by changes in the microphysical and chemical properties with atmospheric transformation. The composition of continental pollution outflow is altered by mixing, an array of chemical reactions, phase changes, and removal processes. Thus, the properties of aerosol and trace gases in downwind regions are impacted by the outflow of pollutants, chemical transformation, and sinks during transport. The importance of addressing the contribution of long-range transported pollutants in air quality legislation has motivated the implementation of the Task Force on Hemispheric Transport of Air Pollutants (HTAP). In the 2010 HTAP report, the Task Force recognizes the significance of intercontinental transport, and recommends further observational studies of long-range transported pollutants to better quantify short-lived climate forcers. To work toward this aim, we propose a combination of new and continued measurements of light absorbing aerosol and co-pollutants at the Pico Mountain Atmospheric Observatory. The Observatory is located in the central North Atlantic, at 2.2 km a.s.l. on Pico Island in the Azores archipelago. The Observatory resides well above the marine boundary layer and receives air characteristic of the lower free troposphere during most times. In previous research, the site has been found to be highly valuable for studying continental outflow that is 3-20 days old and has not been affected by the ocean and local emissions since leaving the continent. Consequently, this site is an ideal location to investigate pollution transport events originating from human activities in North America, from fires in the boreal regions, and occasionally from Saharan dust intrusions. Previous measurements and simulations of dispersion and chemical transport have examined the impacts of outflow from North America on tropospheric ozone and its precursors over the North Atlantic Ocean. In this project, new measurements will be added to the parameters presently measured to address radiative forcing of light absorbing carbon and its co-pollutants. These data will allow us to study the optical properties (absorption and scattering) and composition (hydrophilic and hydrophobic organic carbon, ionic composition, and radioisotope concentrations) of long-range transported aerosols. The measurements will be complemented with an analysis of black carbon and ozone concentrations intercepted at Pico over the last decade. Radiative forcing of light absorbing carbon and its co-pollutants in air masses after long-range transport monitored at the Pico Observatory will be determined by a combination of 3-D chemistry-transport and chemistry-climate models and dispersion modeling.
Post-doc Katja Dzepina, PhD students Simeon Schum and Marian Ampadu, and undergraduate student Senait Gebreeyesus are contributing to this project.
Collaborative Research: Hygroscopic Properties of Aerosol Organics
Aerosols affect the Earth’s radiation balance directly by scattering sunlight and indirectly through their role as cloud condensation nuclei (CCN) (1). An increase in the number of CCN leads to more numerous but smaller cloud droplets and increased cloud albedo. Current estimates of direct and indirect effects, -0.9 to -0.1 and -1.8 to -0.3 W m-2, respectively, remain uncertain because of our inability to accurately estimate the spatial and temporal distributions of aerosol concentrations, size, and composition (2). The “direct” effect is enhanced for hygroscopic aerosols, which absorb water as a function of relative humidity, grow in size, and scatter more light. The indirect effect depends on ability of aerosols to grow into cloud drops (3). Absorption of water vapor by aerosols to produce haze and cloud droplets depends on size and chemical composition of the dry particles.
In this project, we focus on the comprehensive identification of aerosol organic matter components to determine model compounds for input into climate models. Accurate model predictions of the effects of aerosol upon Earth's radiative balance are urgently needed. Structural determination of aerosol organic compounds is quite complex since they are a result of several hundred to a few thousand individual compounds with variable oxygen to carbon ratios. Time resolved sample collection and corresponding analyses will provide useful information regarding the relative significance of the hypothesized model compounds. We are working with investigators at the Desert Research Institute (Drs. Gannet Hallar (Lead PI), Doug Lowenthal, Barbara Zielinska), University of California-Davis (Dr. Simon L Clegg), and Texas A&M University (Dr. Donald R Collins).
MS student Parichehr Saranjampour, PhD student Yunzhu Zhao and undergraduate student Megan Dalbec are contributing to this project.
1) Twomey, S.A., 1974: Pollution and the planetary albedo, Atmos. Environ., 8, 1251-1256.
2) IPCC, Climate Change, 2007: The Scientific Basis, Summary for Policy Makers. IPCC WGI Fourth Assessment Report, approved at the 10th Session of Working Group I of the IPCC, Paris, February 2007.
3) Charlson, R.J. Seinfeld, J.H., Nenes, A., Kulmala, M., Laaksonen, A., Facchini, M.C., 2001: Atmospheric Science-Reshaping the theory of cloud formation, Science, 292, 2025-2026.
MRI: Development of a Turbulent Cloud Chamber
This effort will develop a laboratory cloud chamber to assess impacts of well-characterized turbulence (generated via Rayleigh-Benard convection) on cloud microphysics and aerosol processing. The cylindrical chamber will have a working volume of 3.14 m^3 and be capable of simulating a full range of tropospherically relevant temperatures and pressures (viz. 50 to 20 degC and 10^4 to 10^5 Pa). Supporting instrumentation will allow for generation and detailed characterization of aerosol and cloud particles, measurement of thermodynamic and turbulent properties, and sampling of particles for subsequent chemical and morphological analysis. Topics of immediate interest would include: turbulence, mixing and associated fluctuations of cloud properties; ice processes, including primary nucleation and secondary ice formation; aerosol and cloud chemistry; and both optical and morphological characterization of aerosols. A numerical cloud model will be adapted to simulate and further evaluate processes occurring within the chamber. Aerosol/cloud-particle transformations and the interactive chemical and turbulent processes that influence them are a major focus of this facility. The Intellectual Merit of this work hinges on improved understanding of processes having strong implications for their proper representation of formation of clouds and precipitation, their interactions with aerosol and chemical constituents, and ultimately the role of clouds in the global climate system.
As to Broader Impacts, this comprehensively equipped cloud chamber facility will represent an important addition to U.S. scientific infrastructure for laboratory-based environmental studies, and will be particularly unique in coupling the ability to simulate clouds occurring in a desirably broad range of atmospheric temperatures and pressures with well-characterized turbulence. The chamber will be housed in the new Great Lakes Research Center, which will provide ready access by investigators residing at Michigan Tech and, after time for required initial development and testing, by investigators from across the U.S.
PhD students DM Ashraf Ul Habib and Matthew Brege are contributing to this project.
Identification of Atmospheric Organic Matter by Multi-step Mass Spectrometric Analysis--Completed!
Atmospheric organic matter (OM) associated with aerosol particles significantly influences the chemical and physical properties of aerosol particles. This suggests that atmospheric OM directly modulates the role that aerosol particles play in the atmosphere affecting the Earth's climate. Although uncertain, it appears the combined effects of aerosol particles may lead to a large net reduction in the solar radiation absorbed by the Earth's surface thus masking the true warming of the greenhouse gases (Ramanathan et al., 2001(1)). However, quantifying the magnitude of aerosol impact on climate is much more challenging than quantifying the effects of greenhouse gases. This is largely due to the fact that many aerosols are not directly emitted; rather they are formed in the atmosphere from various precursor gases. Identification of atmospheric OM is urgently needed to assess the chemical effect upon the physical properties of aerosol particles. Atmospheric OM is transformed in the atmosphere by a number of chemical oxidation processes (Poschl, 2005(2) and Rudich et al., 2007(3)). The transformations that increase the ability of aerosol to interact with water are the most crucial; therefore identification is focused on the polar organic compounds. Since oxidation reactions are non-specific, this class of compounds is quite complex and spans the mass range of 100-1000 atomic mass units.
In this project, we focus on uniting the benefits of tandem mass spectrometry (MS) with the power of ultra-high resolution MS for comprehensive identification of atmospheric OM. This will be done using a multi-step approach. The first step includes a pre-screening of collected samples by ultra-high resolution and empirical formula generation. The second step involves development of tandem MS methods using conventional instrumentation (recently acquired). The third step moves the tandem MS analysis to a more powerful platform which includes an ultra-high resolution MS analysis of precursor and fragmented analytes from each MSn generation.
MS Student Jeffrey LeClair contributed to this project.
1) Ramanathan, V., Crutzen, P.J., Kiehl, J.T., and Rosenfeld, D., "Aerosols, climate, and the hydrological cycle," Science, 2001 294:2119-2124.
2) Poschl, U., Atmospheric aerosols: Composition, transformation, climate and health effects. Angewandte Chemie-International Edition, 2005, 44 (46), 7520-7540.
3) Rudich, Y., Donahue, N.M., and Mentel, T.F., "Aging of organic aerosol: Bridging the gap between laboratory and field studies," Annual Reviews, 2007, 58:321-352.
Isotopic Tracer for Climate-Relevant Secondary Organic Aerosol Components--Completed!
Biogenic hydrocarbons, such as alpha-pinene, are oxidized by ozone in the atmosphere, yielding a complex mixture of low volatility compounds that form secondary organic aerosols (SOA). The global annual SOA production from biogenic gases is unknown and is urgently needed for climate prediction models since aerosols are one of the key uncertainties. Because ozone carries a distinct mass-independent isotopic signature (17O), and it is expected that this isotopic signature will be transferred to the secondary products, we are developing new methods to extract this oxygen for stable isotope analysis. The results of these measurements will provide new insights on the mechanisms and amount of SOA that is produced by atmospheric ozonolysis reactions. The 17O signature from ozone is readily found in atmospheric nitrate and is used by many researchers to quantify the source-receptor relationships. However, no method currently exists for analysis of the stable isotopes of oxygen from SOA. We are working with Dr. Thom Rahn and Dr. Rebeka Fisseha at the Los Alamos National Lab to develop an optimized methodology for sensitive measurement of the stable isotopes of oxygen from mixed carbonaceous species generated by controlled ozonolysis of biogenic gases.
Undergraduate research student Annie Putman (2010) and Post-doc Shuvashish Kundu (2010-2011) contributed to this project.